diff --git a/phpseclib/Crypt/Twofish.php b/phpseclib/Crypt/Twofish.php
index 3c1f6dcb..9193e650 100644
--- a/phpseclib/Crypt/Twofish.php
+++ b/phpseclib/Crypt/Twofish.php
@@ -402,7 +402,7 @@ class Twofish extends BlockCipher
             case 256:
                 break;
             default:
-                throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported');
+                throw new \LengthException('Key of size ' . $length . ' not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported');
         }
 
         parent::setKeyLength($length);